The top 20 operations associated with the most expensive hospital stays are listed in the chart below.

When reading, note that by "costliest" the agency means the highest total cost to the health care system. Very common procedures that are inexpensive (e.g., C-sections) rank highly, but less common procedures (e.g., small bowel resection) that are very expensive also make the list.

You can see the average cost-per-stay — how much the procedure costs every time it's done — in the column that's second from the right. (This is the cost to the health care system, which may be different than what patients see on a bill.) Heart valve procedures, which are the 20th most common operating room procedure, had the highest cost-per-stay, clocking in at an average of $53,400.

Perhaps not surprisingly, surgeries are a hugely expensive part of hospital care, accounting for a disproportionate amount of hospital costs. Only about 29 percent of hospital stays involve an operating room procedure, but those stays account for almost half of a hospital's costs.

Hospital pricing also varies dramatically from place to place. One recent report found that uncomplicated births range from $3,000 to $37,000 depending on the hospital.

The AHRQ analysis was intended to "help policymakers and researchers better understand population health and facilitate health care improvement efforts," the authors note.